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Physical Hair Properties Explained: Hair Density, Diameter, Ellipticity, Porosity

Table of Contents

Table of Contents

Learn about the importance of physical hair properties

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Understanding the unique properties of your hair is the key to effective hair care. Your hair possesses distinct characteristics that significantly influence their health and appearance. Taking this into account is the first step towards proper hair care.

The physical properties of hair, such as its curl type, density, ellipticity, diameter, and porosity, collectively shape its distinct characteristics, playing a pivotal role in determining its overall health and appearance.

This article will delve into the factors influencing your hair, offering guidance on tailoring care to its specific needs. Understanding your hair is vital; a deeper comprehension of its science equips you for successful management and styling. Additionally, I sought the expertise of a friend—a hair scientist with a PhD in Chemistry—to enhance the content further.

Decoding Curl Types for Optimal Hair Care

Understanding your hair’s curl type is pivotal for effective care. The Andre Walker Hair Typing System, popularized by celebrity hairstylist Andre Walker in the 1990s, offers a comprehensive classification of hair curl patterns. This system categorizes hair into four main types:

  • Type 1: Straight hair
  • Type 2: Wavy hair
  • Type 3: Curly hair
  • Type 4: Kinky hair

An additional dimension involves defining hair thickness:

  • Level A: Fine hair
  • Level B: Medium hair
  • Level C: Thick hair

Combining these vectors, such as hair 2c, indicates wavy, thick hair. It’s common to have more than one curl type, like 2b curls at the crown and 3a curls in the lower half.

Understanding your curl type facilitates product selection and styling. Opt for products like gels and hairsprays to enhance shape and hold for straight or wavy hair. Kinky hair benefits from extra moisture, making curl butter and leave-in conditioners ideal choices. Importantly, distinguish between hair type and health to tailor your care routine effectively.

How to Determine Your Hair Curl Pattern

Discovering your hair curl pattern is a straightforward process.

  1. Select 1 to 3 strands from your comb and place them on a white surface like paper or a paper towel.
  2. Assess the curl degree and diameter for accurate identification.
  3. Consider using a zoomed-in picture to enhance your observation for a clearer view.
  4. If your hair falls between two curl types, it indicates a combination of both, highlighting the unique diversity of your curls.

Selecting the Right Products for Your Curl Pattern

Choosing the ideal product for your specific curl pattern involves understanding the unique needs of different hair types. Each level has different sebum and moisture content and thus requires different hair care products. Here’s a simplified guide:

Straight Hair (1a, b, or c)

  • Straight hair is prone to being weighed down easily.
  • Opt for products with minimal oils and polymers to avoid build-up and maintain a light feel.
  • Their response to various hairstyles and outdoor air moisture levels (humidity) varies significantly.

Wavy and Curly Hair (2a, b, c | 3a, b, or c)

  • Wavy and curly hair thrives on volume and body.
  • Opt for lightweight products that won’t easily weigh down the curls.
  • Look for coating products that cover the hair shaft, providing hold for your desired style.

Kinky/Coily Hair (4a, b, c)

  • Kinky/coily hair tends to be dry and brittle.
  • Choose products with deep moisturizing ingredients like natural butter (shea, mango, cocoa) and natural oils.
  • Clarification: When we mention “moisturizing” ingredients, we refer to elements retaining moisture.

Understanding these distinctions in hair types allows you to tailor your product choices, ensuring your hair receives the specific care it needs.

Understanding and Styling Based on Hair Density

Hair density - low density versus high density

Understanding the importance of hair density is essential as it influences the tailored care your hair requires. Hair density represents the “number of hair fibers per unit area of the scalp.”1 .

High Hair Density:

  • Indicates a significant amount of hair growth in a small area.
  • Typically associated with thick hair.

Low Hair Density:

  • Suggests fewer hairs growing in the same area.
  • It is commonly found in individuals with thin hair.

Generally, genetic makeup plays a pivotal role in determining hair density. However, factors like environmental conditions, excessive use of chemical treatments, and hormonal changes can contribute to low hair density in cases of hair loss.

Optimal Hair Care Products for Varied Hair Densities

A concentrated hair care formulation is preferable for individuals with high hair density, characterized by a significant number of hair fibers per unit area.

However, this abundance of hair fibers can pose challenges during wet or dry combing. Formulations rich in polymers and emollients are recommended to facilitate detangling and ensure ease of combing.

In contrast, individuals with low hair density benefit from a lighter formulation. It’s best to avoid formulations with high molecular weight polymers, such as polyquaternium 7 & 10 or guar hydroxypropyltrimonium chloride.

Measuring Hair Density with Precision

Determining hair density accurately involves a simple method that requires a friend’s assistance. Follow these steps:

Marking the Scalp:

  • Select a specific area of the scalp.
  • Mark a square, for instance, 1 cm x 1 cm.

Counting Hair Fibers:

  • Count the number of hair fibers within the marked area.

Calculating Hair Density:

  • Use the formula: Hair Density = Number of Fibers / cm2.
  • For instance, if you count 250 fibers in a 1 cm x 1 cm area, the hair density would be 250/cm2.

Repeat for Accuracy:

  • Conduct the experiment in multiple areas on the scalp.
  • Perform three measurements, duplicate the process, and calculate the average.

Remember, a higher number indicates greater hair density in the measured area.

Understanding Hair Ellipticity: Shape and Measurement

Image showing the different ellipticity of hairs.

Hair ellipticity, a crucial aspect of hair structure, refers to the shape of the hair fiber, specifically whether it is round (circular) or elliptical (oval).

The measurement involves assessing the variation in diameter along the x-axis and y-axis. The numerical value for ellipticity is derived from the ratio of these two axes, with a perfect circle having a value of 1.

To gauge ellipticity, it is necessary to calculate the diameter of the hair, providing insights into the unique shape of each strand.2-3

Deciphering Ellipticity: Impact on Hair and Product Selection

Understanding the ellipticity of hair fibers is crucial in guiding product choices for effective care. Hair with high ellipticity, such as kinky coily hair, tends to be more fragile and prone to breakage. For this hair type, specialized care is essential.

Products designed for super curly and coily hair should include higher amounts of moisturizers, emollients, and detanglers. Formulations enriched with natural butter, oils, waxes, and high cationic polymers like polyquaternium 7 or 10 are recommended for optimal results.

On the other hand, Caucasian hair with low ellipticity benefits from a less concentrated formulation. Applying high levels of oils and polymers to such hair can result in greasiness and potential scalp problems, as mentioned earlier.

Hair Diameter: Unveiling Width Variations and Significance

Hair diameter, also known as hair breadth, denotes the width of an individual hair strand, varying across the human population. This measurement, ranging from 17 μm to 181 μm (millionths of a meter), is not an exact science due to the inherent diversity in human hair.

The diameter is influenced by genetic makeup and hair color. Black hair, for instance, tends to be thicker than red hair, with melanin—the pigment responsible for hair color—playing a pivotal role. Higher melanin content contributes to thicker hair strands.

Understanding hair diameter is crucial as it correlates with key factors like strength, flexibility, and elasticity.

conditioner that are specially formulated for dry hair. In addition, try to avoid heat styling whenever possible and use a deep conditioning treatment at least once a week.

By taking these steps, you can help restore your hair’s natural moisture balance and protect it from further damage.

Measuring Hair Diameter: Insights and Ethnic Variations

Hair diameter measurement involves using a microscope, a device designed for precisely measuring small objects. Across different ethnic groups, variations in hair diameter are notable.

Literature reviews reveal distinct diameter ranges for various hair types. For instance, the 1a group, representing straight fine Caucasian hair, typically has an average diameter of 30 – 100 micrometers. In contrast, the 4c group, associated with thick Black hair, demonstrates an average diameter of 45-120 micrometers. However, within these ethnic groups, variations in diameter exist along the hair shaft.

Excessively curly hair exhibits points where the hair is fine and appears flattened, making these areas fragile and susceptible to breakage even with minimal force. The variation in the ratio of two axes at these points determines the value of ellipticity, as depicted in the figure.

Caucasian hair, for example, tends to have an ellipticity of 1.40, while excessively curly hair can have a higher ellipticity, reaching up to 1.89.

Graphic showing the ellipticity of different hair types.

Decoding Hair Porosity: Understanding the Challenge

Hair porosity presents a significant daily challenge, as hair, composed of keratin protein, houses millions of pores along its shaft. The level of porosity is influenced by factors like damage and chemical treatments, resulting in higher pore size. Microscopically, porosity in hair indicates large empty spaces within its cuticular layers.

Highly porous hair has a heightened ability to absorb water and chemicals and is particularly responsive to external humidity. This characteristic manifests in dull, lifeless, frizzy hair with a noticeable lack of shine. Recognizing and addressing hair porosity is key to implementing effective hair care routines tailored to restore vitality and manageability.

How to Determine Your Hair Porosity

Image of the float test.

Determining hair porosity accurately requires a scientific methodology, as at-home trial approaches like the “float test” and “wet test” present empirical results with technical drawbacks.

In the float test, hair strands are placed on the water surface—sinking indicates it is porous (high porosity), while floating suggests non-porosity (low porosity). However, this method is flawed due to factors like water pH, temperature, and the presence of salt, influencing wettability and hence must be maintained.

A more accurate scientific method involves the “weight gain” approach. Hair fibers are calibrated at a constant relative humidity of 65% for 24 hours. Pre-weighed hair samples are then immersed in water under controlled conditions, devoid of salt.

After a specific period, the hairs are removed, dried, and centrifuged to eliminate surface absorbed water. The weight gain (before and after immersion) is calculated and reported as a percentage to determine hair porosity. This method provides a more precise understanding of the hair’s porosity status.4

Traits of Healthy Hair

The health of your hair is intricately connected to your overall well-being, making it a vital aspect of personal health. Healthy hair exhibits key characteristics:

  • It is strong, flexible, and radiantly shiny.
  • Individual strands that are smooth and devoid of damage.
  • The ability to absorb and retain moisture effectively is a hallmark of healthy hair, ensuring optimal hydration.
  • Elasticity is another defining feature, allowing the hair to bounce back to its original shape after being stretched or pulled.
  • Healthy hair is resilient, minimizing the risk of breakage, splitting, or fraying. It remains well-nourished and generally free of build-up.
  • The hair follicles are unobstructed, allowing the strands to grow unimpeded. The scalp is clean and free of debris.

Adopting good hair care habits, such as using gentle shampoos and conditioners and protecting hair from heat damage, is crucial for maintaining its health.

Incorporating regular trims into your haircare routine serves as a preventive measure against split ends and various forms of damage. By consistently caring for your hair, you contribute to its overall health, ensuring it looks and feels its best.


What is the difference between fine hair and thin hair?

Fine hair and thin hair may appear to be the same, but there are some key differences between the two. Fine hair does not imply hair is thin. Fine hair refers to the diameter (width) of the individual strands, while thin hair refers to the density of the hair on the head. Fine hair is also more prone to breakage, which can result in a thinner overall appearance.

In general, those with fine hair need to be gentle when styling or detangling and use products that add body and volume. Those with thin hair may benefit from using products that coat the strands and give the illusion of thicker, fuller hair.

Ultimately, both types of hair require special care and attention in order to maintain a healthy, lustrous appearance.

What is coarse hair?

Coarse hair is a type of hair that is thick, strong, and larger in diameter. It is often difficult to style because it does not hold onto moisture well. This can make it frizzy and difficult to manage.

People with coarse hair often have to use special conditioners and styling products to keep it under control. Coarse hair is usually dry and brittle, so it is important to use products that will hydrate and nourish it.

Deep conditioners are often essential for keeping coarse hair healthy and manageable. In general, people with coarse hair should avoid using heat-based styling tools and focus on products that will help soften and moisturize the hair.

What does the condition or state of hair mean?

The condition or state of your hair can tell a lot about your overall health. For example, if you have dry and brittle hair, it could be a sign that you are not getting enough essential fatty acids in your diet. On the other hand, if your hair is oily and the scalp is flaky, it could be a sign of an overactive sebaceous gland.

While these are just two examples, the condition of your hair can give you insight into your dietary habits and overall health. If you are concerned about the condition of your hair, be sure to talk to your doctor or a qualified nutritionist. They will be able to help you determine whether or not your diet is lacking in essential nutrients.

Can your hair be dry and damaged?

Yes! Dry, damaged hair is a common problem that can be caused by a variety of factors, including over-washing, heat styling, and environmental damage. While damaged hair may look lifeless and dull, it is actually more susceptible to breakage than healthy hair.

The best way to repair dry, damaged hair is to give it some extra TLC. Start by using a shampoo and conditioner that are specially formulated for dry hair. In addition, try to avoid heat styling whenever possible and use a deep conditioning treatment at least once a week.

By taking these steps, you can help restore your hair’s natural moisture balance and protect it from further damage.


1. Zviak, C., The Science of Hair Care. Taylor & Francis: 2005.
2. Syed, A. N.; T, V.; N, S. M., Hair ethnicity and ellipticity: A preliminary studyCosmtics & Toils. 2013.
3. Robbins, C. R., Chemical and physical behavior of human hair. 4th ed.; Springer-Verlag: New York, 2002; p 311-343.
4. Syed, A. N.; Ayoub, H., Correlating porosity and tensile strength of chemically modified hairCosmetics and toiletries 2002, 117 (11), 57-64.


I’m just a girl who transformed her severely damaged hair into healthy hair. I adore the simplicity of a simple hair care routine, the richness of diverse textures, and the joy of sharing my journey from the comfort of my space.

My mission? To empower others with the tools to restore, and maintain healthy hair, and celebrate the hair they were born with!

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